Having assembled a near enough new engine, I was researching breaking-in oils and assembly lubricants to use and came across these threads on general oil usage.
ViscosityAccording to the 3 different aircooled owners manuals, your oil should be based on temperature.
- If the temperature is no less than -15 and no higher than 35, then it says to use 10w30
- If the temperature is no less than 0 and goes above 35, then it says to use 20w40
- The Personal 4 manual says to use 15w40.
Given the UK climate, unless you never use you car when it's near freezing outside, I'd question is it wise to use anything higher than 15w40 in an aircooled?
According to the BIS owner manual it says we should use 15w40.
In fact it even says we can use semi synthetic or mineral 15w40, which leads me to my next topic.
Synthetic vs MineralThe aircooleds were designed with mineral oil in mind, the BIS can take either.
There seems to be a misconception about synthetic oils being thinner, but that's not the whole picture. A 10w40 mineral oil has the same thickness as a 10w40 synthetic oil, if by thickness we're talking viscosity. The difference is, synthetic oils can withstand more pressure before breaking down. For example, when a tappet is pressed up against the camshaft, both oils provide the same thickness between the surfaces. But hypothetically, if that tappet were pressed harder and harder against the camshaft, the mineral oil would break first. Now because many newer engines have greater pressure against various surfaces inside them, they use synthetic oils, thus synthetic gets the reputation of being thinner.
I guess the main point of debate in synthetic vs mineral is the leak factor. There are hundreds of internet forum pages and articles arguing about the legitimacy of this. When researching, I reasoned that if the true answer were obvious or easily proven then we wouldn't even see hundreds of debates on this. Ultimately I seems to comes down to the condition of your engine, more specifically the condition of your oil seals. The older more worn they are, the more likely they are to leak if you use synthetic.
126 oil seals are easy to come by and cheap, what aren't easy to come by (for BIS owners at least) nor cheap, are camshafts and other chunks of the engine... leading to my final section: zddp.
Zinc dithiophosphateZDDP for short, is an anti-wear oil additive that contains roughly equal amounts of zinc and phosphorus and is particularly critical for the correct lubrication of flat-tappet camshafts. The amount of ZDDP has decreased over time with the broad adoption of roller-tappet cams and the negative impact ZDDP has on catalytic converters and the environment.
Most oils have an API approval, with the letter after the S signifying the classification.
- In 1980, the oil standard API SF specified a minimum of 1200 PPM and maximum of 1500 PPM
- API SG reduced the minimum to 1000 PPM and the maximum to 1200 PPM
- API SJ reduced the maximum to 1000 PPM, I can't seem to find a minimum being specified
- By 2004, API SM was introduced and the minimum lowered to 600 PPM, and a maximum of 800 PPM
This isn't a problem for engines as time has gone by, because newer and newer engines become more efficient and better designed against wear. But for old engine with basic flat tappet arrangements, a design that is more prone to wear than a roller tappet, it is a looming problem.
The BIS owner manual specifies API SG (SF if you use mineral), which corresponds to the oil standard at the time of it's introduction. The Aircooled owner manuals
all specify API SE, which was the standard introduced in 1972.
When I was looking up ZDDP, it seems that not longer after API SM was introduced, a wave of flat-tappet camshaft failures were sprouting up. It occurred more in engines where the spring pressure was greater but consensus on forums I've been looking at suggests that once we go below 1000 PPM, cam failures start cropping up. This puts the last "safe" API as SJ... but even then there's no lower limit!
For BIS owners, this may even be a non-issue since the camshaft and tappets are immersed in oil, so long as the oil level is kept topped up:
However for aircooled owners, where the camshaft is above the oil and the engine was designed back when API was down at SE, perhaps it's worth adding some zddp additive, or looking for a classic oil that is SE/SF grade.
Big long article about zddp levels and history of oil etc.